Константы

#include <stdio.h>

int main()
{
    const float PI = 3.141593;
    
    float diameter;
    float radius;
    float circ;
    float area;
    
    printf("Enter the diameter of a circle in millimeters:");
    scanf("%f", &diameter);
    
    circ = PI * diameter;
    radius = diameter / 2;
    area = PI * (radius * radius);
    
    printf("\n\tCircumference is %.2f mm" , circ);
    printf("\n\tAnd the area is %.2f sq.mm\n" , area);
    
return 0;
}